Water Vapour Absorption by the Desert Burrowing Cockroach, Arenivaga Investigata: Evidence against a Solute Dependent Mechanism

1. Solute concentrations were measured in the frontal bodies and hypopharyngeal bladder surfaces, which form the absorption system of Arenivaga. Measured values were compared with the concentrations necessary to lower relative humidity to the absorption threshold, 81% R.H. 2. The predominant inorganic solutes, measured by instrumental neutron activation analysis, were Na, K, and Cl. Their concentrations were 2-3 orders of magnitude below those necessary for absorption. 3. Quantities of a variety of hydrophilic organic molecules were determined with fluorometric reagents. Concentrations of free amino acids, peptides, reducing sugars and polyhydroxyl alcohols were negligible in frontal bodies and on bladder surfaces. 4. Frontal bodies did not appear to be active sites of protein or polysaccharide synthesis, because they did not accumulate significant amounts of radio-labelled amino acids and glucose injected into the hemolymph. 5. The results of this and previous studies indicate strongly that absorption in Arenivaga differs markedly from the solute-dependent schemes which have been proposed for other arthropods.